RFR: 8198949: Modularize arraycopy stub routine GC barriers

[Erik Österlund]

Hi,

The GC barriers for arraycopy stub routines are not as modular as they 
could be. They currently use switch statements to check which GC barrier 
set is being used, and call one or another barrier based on that, with 
registers already allocated in such a way that it can only be used for 
write barriers.

My solution to the problem is to introduce a platform-specific GC 
barrier set code generator. The abstract super class is 
BarrierSetCodeGen, and you can get it from the active BarrierSet. A 
virtual call to the BarrierSetCodeGen generates the relevant GC barriers 
for the arraycopy stub routines.

The BarrierSetCodeGen inheritance hierarchy exactly matches the 
corresponding BarrierSet inheritance hierarchy. In other words, every 
BarrierSet class has a corresponding BarrierSetCodeGen class.

The various switch statements that generate different GC barriers 
depending on the enum type of the barrier set have been changed to call 
a corresponding virtual member function in the BarrierSetCodeGen class 
instead.

Thanks to Martin Doerr and Roman Kennke for providing platform specific 
code for PPC, S390 and AArch64.

Webrev:
http://cr.openjdk.java.net/~eosterlund/8198949/webrev.00/

CR:
https://bugs.openjdk.java.net/browse/JDK-8198949

Thanks,
/Erik